Electronic display device

ABSTRACT

An electronic display ( 2 ) device comprising: a polymer LED display ( 8 ); a filter layer ( 11 ); a semi-transparent reflective layer ( 12 ) covering said filter layer ( 11 ) for transmitting light ( 14 ) emanating from said polymer LED display and for reflecting ambient light ( 13 ) incident on said semi-transparent reflective layer so as to obscure electrical connections for exciting said polymer-LEDs. Due to the reflective properties of the semi-transparent reflective layer ( 12 ), graphics of the polymer LED are hidden while the brightness of the display is maintained to a sufficient degree.

The invention relates to an electronic display device comprising: apolymer LED display comprising a geometrical arrangement of individuallyexcitable polymer LEDs for forming an image, and comprising electricalconnections for exciting said polymer LEDs; and a light-absorbing filterlayer covering said display.

Recently, progress has been made in manufacturing this type of displaydevice, which offers a cost-effective substitute for traditional displaydevices, such as LCD screens or other types of screens. These polymerLED displays exhibit a two-dimensional structure of LEDs which areelectronically controlled by electrodes that are configured to connectto the pixel positions. The electrodes and peripheral electronicconnections form a visible structure in said display that is distractingfor a person reading out said display. Therefore, a need exists toconceal said visible structure, while at the same time maintaining asufficient brightness of the polymer LED display when in use.

In the art, filter layers have been applied with filtering propertiessufficient to hide the underlying graphics of the polymer LED displayand with transmitting properties for transmitting a sufficient amount oflight from the polymer LEDs, in order to achieve a brightness of thedisplay.

However, no sufficient concealment was reached without undue attenuationof light emanating from the polymer LED display. Besides, when filterlayers with insufficient absorbing properties were applied, the graphicsremained discernible. Therefore, due to a relatively strong lightabsorption in the intermediate filtering layer, the known polymer LEDdisplay has quite weak brightness properties, and a desire exists toimprove the readability properties of current polymer LED displays.

The above-mentioned object is solved by a display device according tothe characteristics of the preamble, wherein a semi-transparentreflective layer covers said filter layer for transmitting lightemanating from said polymer LED display and for reflecting ambient lightincident on said semi-transparent reflective layer, so as to obscuresaid electrical connections for exciting said polymer LEDs. When in use,the reflective layer is in a transmissive mode, while, when not in use,the color filter provides a dark background, thus enhancing thereflective properties of the layer. Due to the reflective properties ofthe semi-transparent reflective layer, the graphics of the polymer LEDare hidden while the brightness of the display is maintained at asufficient level.

In a further embodiment, the said semi-transparent reflective layer is areflective polarizing layer. In this embodiment, the losses in thereflective layer due to light absorption are kept optimally low. Such apolarizing layer is known per se from, for example, U.S. Pat. No.6,053,795.

In a further advantageous embodiment, said polymer LED display device,said color filter, and/or said semi-transparent reflective layer arecoupled via an anti-reflective coating. Such coatings generate a higherlight yield by optimizing the transmission of light between theconsecutive layers.

In practical experiments, especially good results were achieved when abrightness-enhancing layer manufactured by 3M Company of St. Paul, Minn.under the trade designation “DUAL BRIGHTNESS ENHANCEMENT FILM” wasprovided as a semi-transparent reflective layer.

It is noted that this layer, referred to as 3M-DBEF film below, is alight enhancement layer which is typically used in connection with aLCD-layer in an LCD-screen. In such LCD-screens, the LCD-layer is oftenilluminated by an electroluminescent light source emitting generallyunpolarized light and situated at the back of the LCD-layer. The 3M-DBEFlayer is a reflective polarizing layer, which reflects the light of theundesired polarization state back into an electroluminescent lightsource. The electroluminescent light source provides a recycling effect,wherein the light reflected back from de DBEF layer into theelectro-luminescent source is returned as light of a generallyunpolarized state. This light is again incident on the polarizing3M-DBEF, thereby increasing the fraction of transmitted light having acorrect polarization state. In the electronic display device accordingto the invention, the reflection of ambient light by this 3M-DBEF layeris quite different from the normal use of this film material, when lightemitted by a back-light is reflected by the 3M-DBEF layer. Furthermore,from U.S. Pat. No. 6,053,795 discloses a configuration with anelectro-luminescent light covered by a color filter and a reflectivepolarizer such as the above-mentioned 3M-DBEF layer. However, thisdisclosure is not concerned with polymer LED displays. Furthermore, thedisclosure describes the use of twofold layers of polarizing filters,wherein a reflective mode is achieved when the two polarizing layershave a predetermined orientation towards each other.

Further advantages and features will become apparent when reading thedescription in connection with the drawings, In the drawings:

FIG. 1 is a perspective view of an electronic device comprising thedisplay according to the invention.

FIG. 2 is a diagram of a polymer LED display according the invention,having a semi-transparent reflective layer.

FIG. 3 is a Table with test results of two embodiments of the invention.

FIG. 1 shows an electronic shaver 1 equipped with the display device 2of the invention. The shaver is a hand-held appliance comprising asynthetic housing 3 accommodating three razor heads 4. In the housing 3,an opening 5 is provided in which the display device 2 is watertightlysealed. The shaver is further provided with a control switch 6 locatedbehind a flexible panel 7 for turning the shaver on or off. In theoff-states, the display device 2 is visually seamlessly integrated inthe wall of the appliance 1, in the on-states, the display device 2 canbe read out in order to identify a battery status and/or current workingstatus of the appliance 1. As a non-limitative example, thedisplay-device may be contained in other, preferably hand-heldappliances, such as mobile phones, gaming devices, etc.

In FIG. 2, a schematic arrangement is shown of the electronic displaydevice 2 according to the invention. The display device 2 has a housing3 comprising a polymer LED display 8. On the polymer LED display 8,functional information may be indicated in the form of graphics/textetc., such as a battery status, time, etc.

In the housing 3 (not shown), various electronic components arecomprised for control and power supply of the polymer LED display 8. Thepolymer LED display comprises electronic connections, such as electrodes9, connecting the individually excitable polymer LEDs 10, which form ageometrical configuration on the polymer LED display 8. In order toconceal these electronic connections 9, the polymer LED display 2according to the invention further comprises a light-absorbing filterlayer 11 covering said polymer LED display 8, for filtering a selectedrange of light emanating from said display. Said filter layer 11provides a relatively dark, light-absorbing background which, incombination with a semi-transparent reflective layer 12 covering saidfilter layer 11, forms a reflective mirror which impairs a view of theinterior of the display device 2. When not in use, the display device 2will look like a mirror, reflecting ambient light 13 that is incident onsaid semi-transparent reflective layer 12.

When the polymer LED display 8 is in use, i.e. when an image is formedon the display 8, the semi-transparent reflective layer 12 will transmitlight 14 emanating from said polymer LED display 8.

For reduction of losses, preferably, the semi-transparent layer 12 is areflective polarizing layer, reflecting light polarized in a firstdirection and transmitting light polarized in a second directionoriented substantially orthogonal to said first direction. Further,preferably, said polymer LED film device 8, said color filter 11, and/orsaid semi-transparent reflective layer 12 are coupled via ananti-reflective coating 15.

In FIG. 3, test results are given for the reflective and transmissiveproperties of two embodiments of the invention. Four tests wereperformed.

In a first test, the transmissive properties of a semi-transparent layerwere tested, wherein the layer consisted of a thin metal film depositedon a transparent substrate. This transmission was tested by measuringthe light output of the polymer LED in the presence and absence ofsemi-transparent reflected layer 12. The transmission of the firstembodiment of the electronic layer is 47%.

Then, the transmissive properties were tested in a second test, wherethe semi-transparent layer used was a brightness-enhancing layermanufactured by 3M Company of St. Paul, Minn. under the tradedesignation “DUAL BRIGHTNESS ENHANCEMENT FILM”. Surprisingly goodresults were obtained with this special film, the transmission in thissecond embodiment was found to be significantly higher, up to 59%.

Likewise, the reflective properties of the display device 2 were tested,comparing the results of the first embodiment and the second embodiment.Again, the reflective polarizing film of 3M turned out to haveespecially good reflective properties as compared with the embodimentcomprising a thin metal film layer.

It will be clear to those skilled in the art that the invention is notlimited to the embodiments described with reference to the drawing butmay comprise all kinds of variations thereof. These and other variationsare deemed to fall within the scope of protection of the appendedclaims.

1. An electronic display device comprising: a polymer LED displaycomprising a geometrical arrangement of individually excitable polymerLEDs for forming an image and comprising electrical connections forexciting said polymer LEDs; and a light-absorbing filter layer coveringsaid display; the display device further comprising: a semi-transparentreflective layer covering said filter layer for transmitting lightemanating from said polymer LED display and for reflecting ambient lightincident on said semi-transparent reflective layer, so as to obscuresaid electrical connections for exciting said polymer LEDs.
 2. Anelectronic display device as claimed in claim 1, characterized in thatsaid semi-transparent reflective layer is a reflective polarizing layer.3. An electronic display device as claimed in claim 1, characterized inthat said polymer LED display, said light-absorbing filter, and/or saidsemi-transparent reflective layer are coupled via an anti-reflectivecoating.
 4. An electronic display device as claimed in claim 1,characterized in that the semi-transparent reflective layer is abrightness-enhancing layer manufactured by 3M Company of St. Paul, Minn.under the trade designation “DUAL BRIGHTNESS ENHANCEMENT FILM”.
 5. Anelectronic appliance comprising an electronic display as claimed inclaim
 1. 6. An electronic appliance as claimed in claim 5, characterizedin that it comprises an electric shaver.